The Destruction of the Sept of Baelor
In this episode, Cersei kills everyone.
Well, not everyone, but pretty close.
Cersei is schedule to be put to trial at the Great Sept of Baelor for the murder of King Robert I, as well as for committing incest. She is, unwisely, permitted to return to her home in the Red Keep while waiting for the trial to take place.
And so, with Cersei being Cersei, she arranges for the enormous store of a magically explosive compound called wildfire to be detonated beneath the Great Sept of Baelor, where the trial was to take place.
At the trial are gathered the majority of Cersei’s enemies, including the popular Margaery Tyrell. When Cersei’s absence is noted, Margaery immediately knows they’re all doomed.
"Cersei understands the consequences of her absence, and she's absent anyway,” she says.
“Which means she does not intend to suffer those consequences. The trial can wait; we all need to leave."
Set to one of the greatest pieces of television music in the past decade, the flame is lit in the bowels of the sept, and vibrant, green flames burst up through the floor, consuming everyone inside and annihilating the building. With it went the entire leadership of the Faith of the Seven, as well as most of House Tyrell.
Clad in all black and watching the flames rise from her balcony, Cersei smiles and drinks from a goblet of wine, cementing herself as one of the greatest television villains ever.